Compression ignition type internal combustion engines such as the two-cycle and more recently four-cycle diesel engines are well known. U.S. Pat. No. 4,539,948, owned by the assignee of the present invention, is a typical example of a two-cycle engine, and the teachings thereof are incorporated herein by reference. Notably, the operation requires use of a glow plug positioned within the combustion chamber near the fuel injector to provide initial ignition of the compressed air/fuel mixture for whatever period of time may be required to bring the engine up to operating temperature.
A glow plug suitable for such use includes a conventional metal sheath-type glow plug capable of bringing the compressed fuel/air mixture to ignitable temperature within a relatively short period of time at ambient temperatures ranging anywhere from -25.degree. F. and upward. Pre-glow time may be as short as 4-6 seconds at relatively high ambient temperatures extending to as much as 24-30 seconds at the lower ambient temperatures, i.e., -25.degree. F. As an assist, it has been known to provide an air-inlet heater, particularly for high power density engines, for starting unaided at temperatures as low as -25.degree. F. and below -25.degree. F. with the glow plug as an additional starting device.
More recently, a great deal of commercial interest and production effort has been shown and expended in the development of ceramic/metal glow plugs and all-ceramic glow plugs. The former includes a metal heating filament, generally tungsten, molded within a ceramic heater element tip, as shown, for example, in U.S. Pat. No. 4,912,305. The latter comprises the use of electrically conductive ceramic particles molded in an all ceramic heating element such as disclosed in U.S. Pat. No. 4,528,121. The development of the ceramic glow plugs, particularly the all-ceramic glow plug, provides a glow plug capable of developing much higher tip temperatures and doing so under a much shorter pre-glow heating period of time.